Coordination of hepatocyte nuclear factor 4 and seven-up controls insect counter-defense cathepsin B expression

In silico promoter analysis and functional validation identify CmZFH, the co-regulator of hypoxia-responsive genes CmScylla and CmLPCAT

Oxygen (O₂) plays an essential role in aerobic organisms including terrestrial insects. Under hypoxic stress, the cowpea bruchid (Callosobruchus maculatus) ceases feeding and growth. However, larvae, particularly 4th instar larvae exhibit very high tolerance to hypoxia and can recover normal growth once brought to normoxia. To better understand the molecular mechanism that enables insects to cope with low O₂ stress, we performed RNA-seq to distinguish hypoxia-responsive genes in midguts and subsequently identified potential common cis-elements in promoters of hypoxia-induced and -repressed genes, respectively. Selected elements were subjected to gel-shift and transient transfection assays to confirm their cis-regulatory function. Of these putative common cis-elements, AREB6 appeared to regulate the expression of CmLPCAT and CmScylla, two hypoxia-induced genes. CmZFH, the putative AREB6-binding protein, was hypoxia-inducible. Transient expression of CmZFH in Drosophila S2 cells activated CmLPCAT and CmScylla, and their induction was likely through interaction of CmZFH with AREB6. Binding to AREB6 was further confirmed by bacterially expressed CmZFH recombinant protein. Deletion analyses indicated that the N-terminal zinc-finger cluster of CmZFH was the key AREB6-binding domain. Through in silico and experimental exploration, we discovered novel transcriptional regulatory components associated with gene expression dynamics under hypoxia that facilitated insect survival.

Insect response to plant defensive protease inhibitors

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

Changes in oxygen and carbon dioxide environment alter gene expression of cowpea bruchids

Hermetic storage is a widely adopted technique for preventing stored grain from being damaged by storage insect pests. In the air-tight container, insects consume oxygen through metabolism while concomitantly raising carbon dioxide concentrations through respiration. Previous studies on the impact of hypoxia and hypercapnia on feeding behavior of cowpea bruchids have shown that feeding activity gradually decreases in proportion to the changing gas concentrations and virtually ceases at approximately 3-6% (v/v) oxygen and 15-18% carbon dioxide. Further, a number of bruchid larvae are able to recover their feeding activity after days of low oxygen and high carbon dioxide, although extended exposure tends to reduce survival. In the current study, to gain insight into the molecular mechanism underpinning the hypoxia-coping response, we profiled transcriptomic responses to hypoxia/hypercapnia (3% oxygen, 17% carbon dioxide for 4 and 24h) using cDNA microarrays, followed by quantitative RT-PCR verification of selected gene expression changes. A total of 1046 hypoxia-responsive cDNAs were sequenced; these clustered into 765 contigs, of which 645 were singletons. Many (392) did not show homology with known genes, or had homology only with genes of unknown function in a BLAST search. The identified differentially-regulated sequences encoded proteins presumptively involved in nutrient transport and metabolism, cellular signaling and structure, development, and stress responses. Gene expression profiles suggested that insects compensate for lack of oxygen by coordinately reducing energy demand, shifting to anaerobic metabolism, and strengthening cellular structure and muscular contraction.